Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a second embodiment thereof.

The broken lines showing the display screen or portion form no part of the claimed design. The remaining broken lines showing text and portions of the graphical user interface form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, substantially as shown and described. 